last modified by: Jake Rothschild

date of last modification: 08/05/2019

Overview

This document will teach JPAL employees the basics of R. This document will focus on the Tidyverse method of programming and the ggplot package for graphics. Please note that while Tidyverse is a commonly used and widely accepted method of R programming, there are other viable methods.

This module focuses on the following uses of R:

  • R Basics
  • Tidyverse Basics
  • Data Cleaning
  • Summary Statistics
  • Data Visualization
  • Regressions and Output
  • R Markdown
  • Functional programming

(I think if this is the only mention, it is good to keep. I agree that is was discouraging with all of the other similar statements.) Before you continue, its worth noting that R has a steeper learning curve than stata. Commands can sometimes be quite particular in their required inputs, and you will need to learn to google for solutions to issues. But, R has payoffs that make this initial difficulty worth it.

Note: Some of the explanations will explain parallels for Stata users, as many JPAL staff will know Stata. It is not necessary to have any Stata background, however.

Some Strengths of R

Both R and Stata have advantages that can make them the better choice for a certain task. Here are features and uses in which R has an advantage.

Visualizations

R’s ggplot package is a state-of-the-art data visualization tool that is constantly being improved by computer scientists and data scientists. Unlike R’s standard plotting package or Stata’s plotting package, ggplot is designed to be an actual langugage of graphics, in which data is logically and non-arbitrarily linked to aesthetics in an iterative manner.

Functional Programming

In Stata, while ado files can be written, the general practice is to write one long script containing many commands. R, especially the tidyverse package, is designed such that it is often best to program in a functional style – long tasks are broken up into medium tasks, and medium tasks are broken up into smaller tasks. This allows for easier debugging, less repetition, less ‘awkward for loops’, and a general better time creating longer, more complex programs.

Storing Multiple Objects

R allows you to store essentially a large number objects – variables, datasets, vectors, and more (R also has a much larger and more specific set of variable types than Stata). This allows you to work with subsets of data or different types of data more easily.

R Markdown

This report is written in R markdown, R’s report format. Using only a couple of small formatting patterns, R automatically transforms code, visualizations, and text into a Latex file, creating a professional and attractive output with minimal user effort.

More Advanced Advantages

Stata is designed to be a basic cleaning and scripting language, with a few simple and powerful commands that make basic econometric work easy. For advanced and resource-intensive statistical techniques, most notably those related to machine learning, R has better tools and is much faster. R is also constantly being improved through open-source programming, while Stata is proprietary and has new packages introduced at a much slower rate.

R Basics

Installing R and RStudio (JPAL Instructions)

Installing R isn’t so straightforward (but is free!), so I would recommend using these instructions to avoid any issues.

Step 1

Step X

In case these instruction were unclear or didn’t work for you, here are online instructions for installing R.

Instructions for installation

Packages

While base R (the available R commands) that don’t require any packages has plenty of useful tools, installing a package is useful for almost any ask. Using a package (in this example, tidyverse) involves the following two commands:

#install.packages(tidyverse)
library(tidyverse)

You may have noticed that install.packages is commented out (in R, # is used for commenting). The reason for this is that once you install a package once, there is no need to do so again. However, for each fresh R session or each fresh use of R Markdown, you will need to run the command ‘library(package)’

For now, I will include only tidyverse and ggplot2, as those will be used throughout this document. However, there are a vast number of packages that will be useful for a host of different tasks.

library(ggplot2)

Importing and exporting data

Importing

The way you import data depends on on the file type you use. Just like Stata, you have to access the correct filepath on your computer. For this tutorial, I created a CSV file called ‘tutorial.csv’. You can go about this either by first changing your directory to the folder like so: Unlike in Stata, you don’t only import the data, but name the data. This is because R can have multiple datasets at once.

#the exact filepath will be unique to each user
setwd("/Users/jakerothschild/Dropbox/BELab - Resources/R/tutorial_files")

#In R, you can use either '<-' or '=' to assign something a value. '<-' is generally considered better style
#read_csv is a command from the tidyverse package. There is also a base R command called read.csv.
tutorial <- read_csv("tutorial.csv")

or by including the entire filepath in the csv command like so:

tutorial = read_csv("/Users/jakerothschild/Dropbox/BELab - Resources/R/tutorial_files/tutorial.csv")

There are a variety of other commands for downloading other filetypes. The pattern is always the same, along the lines of reading_command(filepath), where reading_command varies. Sometimes, you will need to use a package in order to read a certain type of file. A useful example is reading Stata13 files. There is also a file in this folder called ‘tutorial.dta’.

#readstata13 must be installed to read stata13 files. Once again, the install.packages command is commented out because it only needs to be run a single time, while the library command must be ran for each new R session or each new R Markdown compilation
#install.packages("readstata13")
library(readstata13)
#tutorial <- read.dta13("/Users/jakerothschild/Dropbox/BELab - Resources/R/tutorial_files/tutorial.csv")

Now, try importing both the csv and Stata data.

Exporting

Exporting data is quite similar to importing it. You must specify the filepath for your output, and use a specific command to write the file of your choice. This is how I would create a csv file called ‘tutorial.csv’ on my desktop. Unlike Stata, you must specify which dataset is being exported, because R holds multiple datasets.

#The function 'write.csv' takes two inputs: the dataset(in this case, 'tutorial'), and the filepath
write.csv(tutorial, "/Users/jakerothschild/Desktop/tutorial.csv")

Now, try exporting the tutorial dataset to a location of your choice on your computer. You should be able to find and open it.

Variables and Data Management

Variables (Especially useful if you have no coding experience or only in Stata)

In the previous section, R’s ability to hold multiple datasets was discussed. R can actually hold a lot more data than that, but to fully undertstand that we must discuss variables and their different types.

In R, all variables have types. The read_csv command (or any similar command) automatically creates a dataframe. Dataframes are matrixes, in which we generally assume the rows are observations and the columns are variables. However, there are a wide number of data types in R. These include: Vectors Values (The common valuyes are strings(words, characters, etc), integers, True/False, decimal numbers) Tables Functions *Plots and many more. Each data type works differently with different functions.

Most fucntions require specific types for specific inputs. This may seem annoying, but is usually intuitive and helpful. For example, it would make a lot of sense to use the ‘as.numeric’ command on a vector (turning each categorical value in the vector into numbers), but you wouldn’t want to use the command on an entire dataset. By having these more specific data types, it can be easier to understand exactly how a function works.

Here is how to work with some of the basic datatypes.

Values

string <- "Hello World"

num <- 1

#You can assign a variable to another variable, rather than directly assigning it
string2 <- string

#Variables can be reassigned after being initially assigned
string <- "Bye World"

binary <- TRUE

Vectors

#the 'c' command tells R to put the values in commas into a vector
vector_nums <- c(1, 2 ,3)

#it can put different kinds values into vectors
vector_strings <- c("We", "Are", "Coding")


#Vectors can be assigned to other vectors
vector_nums2 <- vector_nums

#Values can be assigned into a vector
one <- 1
two <- 2
three <- 3
vector_nums3 <- c(one, two, three)

#Vectors can be created automatically in many different ways, such as
auto <- c(1:100)


#Vector values can be accessed using indexing. This accesses the 54th element of the vector.
fiftyfour <- auto[54]

Dataframes

#Data Frames are usually imported, not created. However, dataframes can be copied:
tutorial2 <- tutorial

#or created using 'as.data.frame'.

vector_nums <- c(1, 2 ,3)
vector_strings <- c("We", "Are", "Coding")
dataframe_ex1 <- as.data.frame(vector_nums, vector_strings)


#to access a certain variable in a dataframe, use $
id_vect <- tutorial$ID

Data Management And Variables

As you can see, R can hold many different kinds of data at the same time. This can be extremely useful, as it allows you to create many different objects that can used later on. Sometimes this can be used similarly to how you would use a Stata local.

mypath <- "/Users/jakerothschild"
setwd(mypath)

However, there are also some uses that are different from stata. For example, it might be useful to do something like

id_vect <- tutorial$id

#absolute value
id_vect = abs(id_vect)

It can also be quite useful to have multiple dataframes. Imagine that some analyses need to be run on the entire sample, and some need to be run only on women. I can create a dataframe with only women, and work on both that dataframe and my full sample at the same time. You can avoid constantly saving and reloading data, and only save your underlying data to dropbox.

#Don't worry about the syntax used to create the 'women' dataset yet; what is important is that it is possible to do so.
women <- tutorial %>%
        filter(gender == "F")

Tidyverse Basics

Piping

Tidyverse has a very particular syntactic scheme, allowing for avoiding repetition. It uses piping, which allows you to carry through data from one command to the next. Piping will be used throughout the rest of the tutorial

Without Piping

#creating a copy of tutorial to not mess up our original data
tutorial_copy <- tutorial

#we have to say which dataset we are working with in the mutate command
tutorial_copy <- mutate(tutorial_copy, id_squared = id^2)

With piping

#Piping allows us to 'pass in' the tutorial dataset and work with it
tutorial_copy <- tutorial %>% 
                mutate(id_squared = id^2)

Advanced piping

Piping may not seem particularly useful in the previous example. However, it can be quite useful for more complicated processes. Don’t worry about understanding the exact commands used below yet.

Example without piping

#creating a copy of tutorial to preserve original dataset
tutorial_copy <- tutorial

#creating new variables
tutorial_copy <- mutate(tutorial_copy, score_squared = score^2)
tutorial_copy <- mutate(tutorial_copy, score_squared_bucket = ifelse(score_squared < 100, 0, 1))

#creating a grouped dataset
tutorial_groups <- group_by(tutorial_copy, score_squared_bucket)

#summarizing the grouped dataset
tutorial_summary <- summarize(tutorial_groups, avg_score = mean(score_squared))

Example with piping

#we start by saying that our new dataset, tutorial summary is equal to tutorial
tutorial_summary <- tutorial %>% 
              #but by piping, we tell r that we are still working with the tutorial dataset
              #so we don't need to include tutorial in our commands again
              mutate(score_squared = score^2) %>%
               mutate(score_squared_bucket = ifelse(score_squared< 100, 0, 1)) %>%
                        #here, we group by a certain variable (this is equivalent to bysort in stata)
                        group_by(score_squared_bucket) %>%
                        #now, because of piping, we are working with the grouped version of the dataset.
                        summarize(avg_score = mean(score_squared))

As you can see, piping allows us to use less keystrokes, create less datasets, and (although it may not seem it at first) create clearer code

Data Cleaning

The vast majority of cleaning operations can be done using a few simple commands.

Removing observations

The basic tidyverse method for removing observations is the filter command. Filter only keeps observations where the condition is met for that variable.

Basic Conditions

#creating a copy to not change original dataset
  tutorial_copy <- tutorial

  #piping is used to work within the tutorial dataset
  tutorial_copy <- tutorial_copy %>%
            #only keeping observations where gender is equal to f
            filter(gender == "F")

Logical statements can be used for different types of filtering complicated ###More conditions

#creating a copy to not change original dataset
  tutorial_copy <- tutorial

  #piping is used to work within the tutorial dataset
  tutorial_copy <- tutorial_copy %>%
            #only keeping observations where gender is equal to M or F
            filter(gender == "F"|gender == "M")
  
    #restoring tutorial copy
    tutorial_copy <- tutorial
  #piping is used to work within the tutorial dataset
  tutorial_copy <- tutorial_copy %>%
            #only keeping observations where gender doesn't equal F
            filter(gender != "F")

Removing variables

To choose variables to keep, we use the select command.

tuturial_copy <- tutorial

tutorial_copy <- tutorial_copy %>% 
                 select(gender, score)

To remove variables, use the identical command but with ‘-’ before variables we wish to remove

tuturial_copy <- tutorial

tutorial_copy <- tutorial_copy %>% 
                 select(-gender, -score)

New Variables

To create new variables, use the mutate command. Multiple variables can be created at once with this command

tutorial_copy <- tutorial

#just one variable
tutorial_copy <- tutorial_copy %>% 
                 mutate(score_x_2 = score * 2)

##multiple
tutorial_copy <- tutorial_copy %>% 
                 mutate(score_x_4 = score * 4,
                        score_x_3 = score * 3)

ifelse is a very useful command for creating categorical variables. It takes three arguments: a condition and two outcomes. It then assigns variables to the first outcome if it meets the condition, and to the second outcome if not.

tuturial_copy <- tutorial

#this command creates the variable score_greaterthan_10. This variable is equal to 1 if score is > 10, and 0 if score < 10
tutorial_copy <- tutorial_copy %>% 
                 mutate(score_greaterthan_10 = ifelse(score > 10, 1 , 0))

Nested ifelse statements can create more than two buckets. There are some other commands that can do this more efficiently, depending on the specific task, but that is beyond the scope of this tutorial.

tuturial_copy <- tutorial

tutorial_copy <- tutorial_copy %>% 
                #The first ifelse states that if score is <10, score_buckets should be equal to 0, but if score is > 10, we should go into a second ifelse statement.
                 mutate(score_buckets = ifelse(score < 10, 0 ,
                                               #the second ifelse only is read if the first ifelse condition isn't met. It tells us that we should set score_buckets to 1 if score is between 10 and 20, and 2 otherwise.
                                               ifelse(score >= 10 & score < 20, 1, 2)))

Renaming Variables

Renaming variables is simple. Use the rename command

tutorial_copy <- tutorial

tutorial_copy <- tutorial_copy %>% 
                rename(identification = id)

Reshaping

Sometimes, it will be important to change the format of your data from wide to long or long to wide. A long dataset changes the unit of analysis such that each row contains less data, and as a result, there are more rows. This example should show the difference. Note that both datasets show the exact same information. However, it is usually much easier to work with one type of data, depending on the task at hand.

Wide to long

Gather is used to reshape data from wide to long. This transformation tends to be more common. Currently, each row contains two scores: score and score2. When we reshape the data to long, we will have create a new variable, ‘round’, that tells us which type of score the data is. So, each row will only contain one score instead of two, which means that then number of rows will double.

The gather command takes 4 arguments; 1)The dataset, which in this case is piped 2)A key string, which is the name of the column used to distinguish between the different types of values 3)A value string, which is the name of the column of the combined outcome variable, in this case score 4)A vector, which contains the columns that should be combined into 1, in this case score

tutorial_long <- tutorial %>%
              gather("score_type", "score", c(score, score2))

While in this example we use only a single column, gather can be used for multiple columns. Gather isn’t the easiest command to use, so make sure you know exactly what you want your data to look like before using it.

Long to wide

Spread is the command used to reshape data from long to wide. In the tutorial_long dataset, there should now be 12 observations of the dataset. We will shift it back to its original form using spread.

Spread takes three arguments: 1)The dataset, which in this case is piped 2)A key, which is the variable in the dataset that describes which type of data it is. In this case, it is score_type, as it distinguishes between score and score2 3)A value, which is the variable that contains the information, which in this case is score.

tutorial_wide <- tutorial_long %>%
                spread(score_type, score)

Now, each row contains two observations, one of each score type. Similarly to gather, this commmand can be tricky to use, and you must have a clear understanding of your data.

Missing Values

In R, is.na(variable) evaluates to true if the variable is missing. !is.na(variable) does the opposite.

tutorial_copy <- tutorial

tutorial_copy <- tutorial_copy %>% 
                mutate(missing_id = is.na(id))

tutorial_copy <- tutorial_copy %>% 
                mutate(non_missing_id = !is.na(id))

Datasets: Altering or Creating New

In all of these examples, I have been creating a copy of my dataset and then changing that copy. That is unnecessary in R. For example, to create a tutorial_copy dataset with a missing_id variable, I can simply do:

tutorial_copy <- tutorial %>%
             mutate(missing_id = is.na(id))

However, I could also simply adjust my original tutorial dataset. While the ability to hold multiple datasets at once is a convenient feature of R, that doesn’t mean you want to create a new dataset with every single change. It is up to the user to figure out how to create protocols for when to create a new dataset, and when to adjust an old one.

Summary statistics

R has somewhat more challenging syntax than stata for summary statistics, but also allows for a greater level of customization in choice of summary statistics. You can also easily create and work with summary statistic datasets, which tends to be a poor opton in Stata.

Summarize

Summarize is the main tidyverse tool for both looking at summary statistics and creating summary datasets. Like other tidyverse commands, it works best with piping. A variety of statistics, such as mean, minmax, number of observations, standard deviation, and more can be calculated this way.

##We can create one specific summary statisitcs
tutorial %>%
  summarize(avg_score = mean(score))
## # A tibble: 1 x 1
##   avg_score
##       <dbl>
## 1        26
##Or multiple
tutorial %>%
  summarize(avg_score = mean(score), sd_score = sd(score))
## # A tibble: 1 x 2
##   avg_score sd_score
##       <dbl>    <dbl>
## 1        26     18.4
##We can use filter to summarize conditionally
tutorial %>%
  filter(score > 5) %>%
  summarize(avg_score = mean(score), sd_score = sd(score))
## # A tibble: 1 x 2
##   avg_score sd_score
##       <dbl>    <dbl>
## 1        31     15.4
##We can create a dataset of summary statistics
tutorial_summary <- tutorial %>%
  summarize(avg_score = mean(score), sd_score = sd(score))

group_by

‘group_by’ is similar to Stata’s ‘by’ command. It splits data into a bunch of smaller chunks, and then applies the next set of code to each chunk individually. This allows you to get group counts, similar to tab.

##Standard count of gender
tutorial %>% 
  group_by(gender) %>%
  summarize(count = n())
## # A tibble: 2 x 2
##   gender count
##   <chr>  <int>
## 1 F          2
## 2 M          4
##Can do multiple groups
tutorial %>% 
  group_by(gender, position) %>%
  summarize(count = n())
## # A tibble: 4 x 3
## # Groups:   gender [2]
##   gender position   count
##   <chr>  <chr>      <int>
## 1 F      Rassistant     1
## 2 F      Rassociate     1
## 3 M      Intern         2
## 4 M      Surveyor       2
##And can filter
tutorial %>% 
  filter(score > 10) %>%
  group_by(gender, position) %>%
  summarize(count = n())
## # A tibble: 4 x 3
## # Groups:   gender [2]
##   gender position   count
##   <chr>  <chr>      <int>
## 1 F      Rassistant     1
## 2 F      Rassociate     1
## 3 M      Intern         1
## 4 M      Surveyor       2

We can go beyond counts and get group means, maxs, etc

##Mean Score By Gender
tutorial %>% 
  group_by(gender) %>%
  summarize(mean = mean(score))
## # A tibble: 2 x 2
##   gender  mean
##   <chr>  <dbl>
## 1 F       41.5
## 2 M       18.2
##With Filtering
tutorial %>% 
  filter(score > 10) %>%
  group_by(gender) %>%
  summarize(mean = mean(score))
## # A tibble: 2 x 2
##   gender  mean
##   <chr>  <dbl>
## 1 F       41.5
## 2 M       24

group_by is useful for creating new summary statistic datasets. Many of the ggplot commands work much better with data in this format

gender_means <- tutorial %>% 
  group_by(gender) %>%
  summarize(mean = mean(score))

Data Visualization

ggplot

ggplot is an R package designed to be a ‘grammar of graphics’. This means that rather than memorizing syntax for a given output, creating ggplots requires thinking about how to map data onto different visual features. This allows for much greater control of graphics and for more logically created graphics. For more information about the philsophy of ggplot, read this
The ggplot command requires two inputs: data and aesthetics, although you will almost always want to include geoms, and often themes, labels, and scaling Through this section, we will iteratively build a beautiful plot.

Aesthetics

Aesthetics describe how your data is being mapped onto a physical plot (what this means may be unclear at first, so hang in there). Every ggplot requires at least one aesthetic, but more can be used.

#aes is short for aesthetics
p <- ggplot(data = tutorial, aes(x = score, y = score2))

p

As you can see, the x axis is score, and the y axis is score2. This is what aesthetics does; it takes a variable from the dataset and maps that variable onto a feature of the graph. In this case, we only use two axes, but much more is possible.

Geoms

We currently have an empty graph, which isn’t telling us much of anything. What we now want to do is add a geom, which are different kinds of physical shapes that represent the data that has been mapped to aesthetics.

#to add features to a ggplot, we use +
p <- p + geom_point()

p

You can use different kinds of geoms, still using the same aesthetics

#resetting p
p <- ggplot(data = tutorial, aes(x = score, y = score2))

#don't worry about the syntax, but this adds a regression line
p <- p + geom_smooth(method = 'lm',se = F)

p

You can, and often should use multiple geoms on the same graph

#don't worry about the syntax, but this adds a regression line
p <- p + geom_point()

p

There are also some aesthetics that work best with geoms. For example, now we can add in gender as a third aesthetic, and map it to color

p <- ggplot(data = tutorial, aes(x = score, y = score2, color = gender)) +
  geom_point() +
  geom_smooth(method = 'lm', se = F)

p

If you want some geoms to have aesthetics but not others, you can use aes in the geom itself, rather than the ggplot command. In this plot, the points are colored by gender, but we only have a single regresion line.

p <- ggplot(data = tutorial, aes(x = score, y = score2)) +
  geom_point(aes(color = gender)) +
  geom_smooth(method = 'lm', se = F) 

p

As you can see, with just the basic structure of aesthetics and geoms, you can build more and more complex plots. You are also able to build iteratively, as you can start with single aesthetics and geoms, and add and take away features until your data is shown most clearly.

Some common geoms are: * geom_point (points for scatterplots) * geom_smooth (estimate lines, can be linear or nonlinear) * geom_bar (bar charts) * geom_density (density plots) * geom_histogram (histograms) * geom_abline (unfitted lines, for example to show what a linear relationship would look like) * geom_errorbar (error bars) * geom_text (for labeling bar chart estimates, for example)

Scales

By default, ggplot scales the graph to the data, so p is scaled from 0-50 on the x axis, and 0-40 on the y axis. If we assume that score and score2 are similar in nature, we would want them to be scaled identically, or we may mislead the audience. To do this, we use the command scale_AESTHETIC_SCALING, where in this case AESTHETIC is y, and SCALING is continous.

p <- p + scale_y_continuous(limits = c(0, 50))

p

Any aesthetic can be changed using the scale command, and you will have the options of continous, discrete, or manual, depending on the type of data.

Labels and Legends,

Our graph, p now does depict certain aspects of our data. However, it isn’t very clear what exactly it is showing, as there is no title, and the legend and axis labels are based on the data, and therefore unclear. The main command used for labeling is labs, which can affect the title and any aesthetics.

p <- p + labs(title = "Scores By Gender", x = "Score 1", y = "Score 2", color = "Gender")

p

We can also change the legend labels using the scale command from the previous section.

p <- p + scale_color_discrete(labels = c("Female", "Male"))

p

Themes

Now, all that is left to do is make the graph look nicer. To do this, we use the theme command. There are dozens of options that can be used for the theme command, so you will have to figure out for yourself what you think works best. The syntax is straightforward; this is how you would remove the panel grid.

p <- p + theme(panel.grid = element_blank())

p

The best practice is to create a theme and then use it across all charts. This is another situation in which R’s flexibility in storing objects is very useful. For example, we can create a theme like so.

my_theme <-  theme_bw() + 
  theme(text = element_text(size = 10, face = "bold", color = "black"),panel.grid = element_blank(),axis.text = element_text(size = 10, color = "gray13"), axis.title = element_text(size = 10, color = "black"), legend.text = element_text(colour="Black", size=10), legend.title = element_text(colour="Black", size=7), plot.subtitle = element_text(size=14, face="italic", color="black"))

And then use it for not only this graph, but all later graphs

p <- p + my_theme

p

It is even possible to have your theme be a function, which allows you to customize your theme for different situations, but that is a more advanced topic and unneccessary for creating excellent ggplots.

Data Types

One thing that may happen to you as you try creating ggplots is that you sometimes have hard-to-understand errors or create useless graphs. For example,

bad <- ggplot(data = tutorial, aes(x = gender)) + geom_density()

bad

is entirely meaningless,

while

#error <- ggplot(data = tutorial, aes(x = gender)) + geom_bar(stat = 'identity')

#error

gives you an error, even though the syntax is accurate (commented out to avoid having the file crash). This is because certain plots only work with certain kinds of data. For example, a bar chart will work best with one continuous variable and one categorical variable. Scatterplots work well with two continuous variables. Whether a misuse of a variable results in an error or a bad graph depends on the specific type of error, but either way, you need to understand your data before trying to visualizate it.

Advanced ggplot

Once you have gotten comfortable with ggplot, there are some more complicated packages that can be used alongside ggplot to create some more advanced graphics.

These include

  • shiny – allows you to create interactive dashboards, like this
  • ggmap – for creating and customizing maps
  • ggraph/dendextend – For higher-dimensional data, can create network plots, dendrograms

Examples and more info

Here are some articles that have more examples of ggplot syntax and technique, along with some more information about the package. 1) 2) 3)

Regressions

Basic Regressions

A standard linear regression uses the command lm takes two arguments: A formula and data. The syntax works as follows

reg <- tutorial %>%
  #score is the dependent variable, score2 is the independent variable. Our formula is score = B(score2) + error
  #data = , is used because we pass in the tutorial dataset using piping
  lm(score ~ score2, data = .)

We can use multiple independent variables/controls using the same syntax, with + separating different regression inputs in the formula.

reg_gend <- tutorial %>%
  #In this case, our formula is score  = B1(score2) + B2(gender) + error
  lm(score ~ score2 + gender, data = .)

And we can measure interaction effects using * in our formula.

reg_gend_interation  <- tutorial %>%
  lm(score ~ score2 + gender + score2*gender, data = .)

Output

You may have noticed that there hasn’t been an output from the previous regressions. This is because all we did is create the regression object. There are a few ways to see regression results.

The easiest of these is summary. When using regressions for

summary(reg)
## 
## Call:
## lm(formula = score ~ score2, data = .)
## 
## Residuals:
##       1       2       3       4       5       6 
##  -4.034  17.144 -14.856  14.339 -22.246   9.653 
## 
## Coefficients:
##             Estimate Std. Error t value Pr(>|t|)
## (Intercept)  14.4070    13.2286   1.089    0.337
## score2        0.4830     0.4561   1.059    0.349
## 
## Residual standard error: 18.2 on 4 degrees of freedom
## Multiple R-squared:  0.219,  Adjusted R-squared:  0.02377 
## F-statistic: 1.122 on 1 and 4 DF,  p-value: 0.3493

We can also use summary directly, without creating a regression object.

tutorial %>%
  lm(score ~ score2 + gender + score2*gender, data = .) %>%
  summary
## 
## Call:
## lm(formula = score ~ score2 + gender + score2 * gender, data = .)
## 
## Residuals:
##          1          2          3          4          5          6 
##  4.080e+00  1.998e-15 -4.690e+00 -4.441e-16 -1.597e+01  1.658e+01 
## 
## Coefficients:
##                Estimate Std. Error t value Pr(>|t|)
## (Intercept)     31.7561    18.1347   1.751    0.222
## score2           0.4146     0.5815   0.713    0.550
## genderM        -27.8397    24.9512  -1.116    0.381
## score2:genderM   0.1764     0.8466   0.208    0.854
## 
## Residual standard error: 16.86 on 2 degrees of freedom
## Multiple R-squared:  0.6648, Adjusted R-squared:  0.1621 
## F-statistic: 1.322 on 3 and 2 DF,  p-value: 0.4579

When we create a regression and store it as an object, we have created a list that contains tables. When including regression output in a report, using a table display package such as kableExtra is the best method of outputting the results. The syntax is somewhat complicated, so it will not be included in this document. A quick internet search will provide examples and guides like this one.

Other regressions

Other regressions usually require a package, but use the same syntax as lm. For example, for a fixed effects regression, one must install the lfe package, and use a similar command to above, but with ‘felm’ replacing ‘lm’. For a logistic regression, the glm package is required, and ‘glm’ replaces ‘lm’ in the above commands. There are more regression types and packages than can be employed for the circumstance.

Functions

Why use functions

Syntax

Examples

R Markdown

This document was created entirely in R Markdown, R’s document creating tool. Using R Markdown is incredibly simple and straightforward. In the Rstudio interface, click on File -> New File -> R Markdown. It will open up a tab in which you can input the author, title, and output (these can all be changed later). After clicking OK, a new tab will appear. It should look something like this

The way R Markdown works is that it doesn’t treat text as code unless specifically instructed too. So, if you write a command like read_csv(filepath), and then try to run it, nothing will happen. To create R code, use the following structure

This way, you can switch back and forth between plain text like this

print("and code like this")
## [1] "and code like this"

When you want to see the output of your RMD script, you click the knit button on the Rstudio interface. You can then choose to knit to html, word, or pdf. There is no cost of knitting, so I suggest you knit early and often to make sure that everything is working.

Once you have a document you like, there are various publishing options. Most only work with html, which tends to be the most compatible with R Markdown in general.

There are also a variety of advanced options for R Markdowns. These include creating a table of contents, putting different outputs into tabs to reduce the length of your report, hiding code so reports only show output and text, and a host of text formatting tools.

Team projects, working across files, etc

Cheat sheet of useful commands

This is not a complete list. To do other things, you will often need to google, but R is quite well-documented.

Installing packages

  • install.packages: Only run this once to install a new package

install.packages(“package”)

  • libaray: Will need to be used every new R session and every new RMD knitting *

*library(package)

Importing/exporting

  • read_csv: Read CSV File

    new_data <- read_csv(filepath)

  • write_csv: Write CSV Files

    output <- write_csv(filepath)

  • other data-specific commands: Read/Write Non-CSV Files

    new_data_from_dta <- read.dta13(filepath)

Cleaning/changing structure

  • select: Keep Or Drop Variables

    data <- data %>% select(variables to keep)

  • filter: Keep Or Drop Observations

    *data <-  data %>%*
*filter(condition)*

  • group_by/summarize: Work Within Group Of Data, Create Summary Datasets

    *group_mean_dataset <- original_data %>%*
                      *group_by(variable1) %>%*
                      *summarize(mean_variable2 = mean(variable_2))*

  • gather

    tbd when I learn the syntax

  • spread

    tbd when i learn the syntax

Creating new variables

  • mutate: Create New Variable

    data <- data %>% mutate(var_squared = var^2)

  • ifelse

    data <- data %>% mutate(binary_variable = ifelse (variable > x, 1, 0))

Summary Statisitcs

  • summarize: Summarize Number Of Observations, Means, More

    data %>% group_by(x) summarize(n_obs = n())

    data %>% group_by(x, y) summarize(n_obs = n())

    data %>% filter(y > 100) %>% group_by(x) %>% summarize(n_obs = n())

    *data %>%*
*group_by(x)*
*summarize(mean_y = mean(y), sd = sd(y))*

Regressions

  • lm: Linear Regression

    simple_regression <- data %>% lm(dv ~ iv, data = .)

    controlled_regression <- data %>% lm(dv ~ iv + control, data = .)

    interaction_regression <- data %>% lm(dv ~ interaction_var1 * interaction_var2, data = .)

  • felm: Fixed Effects Linear Regression

    simple_regression <- data %>% felm(dv ~ iv, data = .)

    controlled_regression <- data %>% felm(dv ~ iv + control, data = .)

    interaction_regression <- data %>% felm(dv ~ interaction_var1 * interaction_var2, data = .)

  • summary: Display regression results

    data %>% lm(dv ~ iv, data = .) %>% summary()

Visualizing

  • ggplot

ggplot(data = dataset, aes(x = xaxis_var, y = yaxis_var, color = grouping_var))

  • geom_bar/point/smooth/histogram/density/more

ggplot(data = dataset, aes(x = xaxis_var, y = yaxis_var, color = grouping_var)) + geom_point(color = “manual_color”, aes(size = variable_from_dataset))

  • labs

    ggplot(data = dataset, aes(x = xaxis_var, y = yaxis_var, color = grouping_var)) + geom_point(color = “manual_color”, aes(size = variable_from_dataset)) + labs(title = “Title”, x = “X Axis Label”, y = “Y axis Label”)

Functions

  • function_x <- function(input1, input2= 0, input_x){ Function body goes here }